It is well known to provide a flexible thermoplastic sheet inclusive of plastic film with a plurality of fine pores and thereby to make the sheet air-permeable. The porous plastic sheet formed in this manner usually has slimy gloss and sticky touch characterizing the plastic sheet which are disliked by users in some applications of the sheet. To alleviate such gloss and to improve the touch of the sheet, several techniques have already been proposed, for example, the technique by which the sheet surface is embossed to take the gloss off and simultaneously to provide the surface with irregularities and pores, and the technique by which a third ingredient having delustering effect as well as pore forming effect is previously mixed into raw material for the sheet so that desired delustering and pore forming effects may be achieved on a step of sheet production.
However, these well known techniques have not been able to achieve a satisfactory improvement of the plastic sheet particularly for such plastic sheet used as a topsheet of disposable hygienic wearable articles such as a sanitary napkin and a disposable diaper, because said gloss and touch of the topsheet of such hygienic wearable articles, which are destined to be in direct contact with wearer's skin, are decisively disliked. U.S. Pat. No. 4,342,314 discloses a technique to provide a flexible plastic sheet with a fibrous appearance and capillary structure. This technique also intends to alleviate the sticky touch usually characterizing the plastic sheet, but the sheet obtained by this technique is considered to have a smooth surface and rather slimy gloss because of its smoothness.
Accordingly, it is a principal object of the present invention to alleviate said gloss and undesirable touch conventionally characterizing the plastic sheet by providing the plastic sheet with air-permeable vacant spaces defined by ribs crossing one another so that these ribs and vacant spaces may cooperate together to create an appearance like woven fabric.